1. Field of the Invention
This invention relates to a hard disk apparatus including a semiconductor laser as a light source for carrying out thermally assisted magnetic recording and a driving method for the hard disk apparatus.
2. Description of the Related Art
FIG. 1 shows an example of a configuration of a hard disk apparatus.
Referring to FIG. 1, the hard disk apparatus 1 is roughly divided into four sections including a head disk assembly 2, a signal processing circuit 3, a motor driver 4 and a system controller 5 in the form of a microcomputer for controlling the overall system.
The head disk assembly 2 includes a magnetic disk 21 for storing information, a spindle motor 22 for rotating the magnetic disk 21, a recording head 23 and a reproduction head 24 for carrying out recording and reproduction of information on and from the magnetic disk 21, respectively, a read/write amplifier 25 and so forth.
The head disk assembly 2 is configured by integrating the mechanism parts described, a voice coil motor 26 and so forth.
The recording head 23 and the reproduction head 24 are mounted at a tip end of a carriage for movement in a radius direction on the magnetic disk 21. The carriage is driven by the voice coil motor 26.
A write amplifier 25W for driving the recording head 23 and a read amplifier 25R for amplifying a signal from the reproduction head 24 are formed from one IC normally as the read/write amplifier 25.
In order to cope with increase of the transmission rate in recent years, also the read/write amplifier 25 is mounted on the carriage in order that the wiring line length to the recording head 23 and reproduction head 24 may be minimized.
The signal processing circuit 3 includes a modulation circuit 31, a recording compensation circuit 32, a read channel circuit 33, a servo data detection circuit 34, an ECC encoding scramble circuit 35, an ECC decoding descramble circuit 36 and a host apparatus interface (I/F) 37.
The signal processing circuit 3 further includes an SDRAM 38 and a recording clock section 39.
The signal processing circuit 3 produces recording data from user data sent thereto from a host apparatus, and reproduces user data from a reproduction signal and transmits the reproduced data to the host apparatus.
The signal processing circuit 3 carries out processes such as addition of an ECC code, encoding and scrambling for user data sent thereto from the host apparatus. The modulation circuit 31 produces recording data synchronized with a recording clock and transmits the produced data to the write amplifier 25W.
The write amplifier 25W drives a magnetic field head with recording current designated by the system controller 5 in accordance with the recording data to generate a modulation magnetic field.
In high-density recording in recent years, a phenomenon appears that a flux reversal position is displaced by an influence of magnetic domains generated adjacent to each other, and a technique for compensating for the displacement by the recording compensation circuit 32 is used.
The read channel circuit 33 carries out signal processes based on the PRML (Partial Response Maximum Likelihood) method such as waveform equalization, Viterbi decoding and demodulation for the reproduction signal sent thereto from the read amplifier 25R.
The signal is further subjected to such processes as descrambling, decoding and error correction to produce user data.
While only a servo signal processing section is shown in FIG. 1, the system controller 5 controls the entire system in accordance with an operation command designated from the host apparatus.
Servo data detected from within the reproduction signal is transmitted to the servo signal processing section 51 to control the voice coil motor 26 and the spindle motor 22.
The motor driver 4 drives the voice coil motor 26 and the spindle motor 22 in accordance with instructions from the servo signal processing section 51.
[Zone Bit Recording]
Now, zone bit recording is described.
In the hard disk apparatus 1, the magnetic disk 21 is rotating at a constant speed of rotation.
Since the linear velocity, that is, the relative speed between the head and the medium, increases toward the outer periphery of the magnetic disk 21, if recording is carried out with a constant channel clock frequency, then the linear density decreases toward the outer periphery.
Therefore, as shown in FIG. 2A, one disk is divided into a plurality of zones in which channel clock frequencies are different from each other.
Then, the channel clock frequency is increased toward a zone on the outer periphery side as seen in FIG. 2B to avoid drop of the linear density and increase the information amount which can be stored on one disk.
While the channel clock frequency is constant in one zone, the linear velocity and the linear density gradually vary depending upon the radius.
[Thermally Assisted Magnetic Recording]
Now, thermally assisted magnetic recording is described.
The risk for data loss by a thermal fluctuation increases together with increase of the recording density, and thermally assisted magnetic recording is proposed as a countermeasure against the risk (for example, refer to Japanese Patent No. 3932840).
The thermally assisted magnetic recording is a method wherein a medium having high coercive force is used to avoid the problem of the thermal fluctuation.
The high coercive force medium cannot be recorded by a popular recording head.
If a very small light spot is irradiated to increase the medium temperature, then the coercive force can be decreased and recording can be carried out by a recording head similar to that of an existing technique.
A small semiconductor laser whose emergent light is uniform in wavelength and phase is suitable as a light source for producing a very small light spot.
FIG. 3 illustrates a manner of a medium in thermally assisted magnetic recording.
An exiting recording method has a problem that, if the recording head is reduced in size in order to increase the recording density, then a magnetic field which can be generated thereby becomes so small that a magnetic field necessary for recording cannot be obtained.
In this method, by forming a very small light spot, a magnetic domain smaller than the recording head corresponding to the light spot can be formed and the recording density can be increased in both of a linear direction and a track direction.
FIGS. 4A and 4B show a recording magnetic field and an optical waveform in the thermally assisted magnetic recording, respectively.
The recording magnetic field shown in FIG. 4A is an alternating field in accordance with recording data similarly as in normal magnetic recording.
On the other hand, a light spot shown in FIG. 4B is intermittently irradiated in a cycle of a channel clock.
A magnetic domain in accordance with the recording magnetic field is formed in a region in which the medium temperature is increased and the coercive force is decreased by the light spot.
The waveform of the light spot determines not only a temperature distribution of the medium but also the shape of a magnetic domain to be formed.
Accordingly, in order to implement high-density recording, not only the phase of the light waveform with respect to the recording magnetic field but also the pulse width and the light power with respect to the recording magnetic field must be suitably controlled.